hgweb: also set Content-Type header
Our HTTP/WSGI server may convert the Content-Type HTTP request
header to the CONTENT_TYPE WSGI environment key and not set
HTTP_CONTENT_TYPE. Other WSGI server implementations
do this, so I think the behavior is acceptable.
So assuming this HTTP request header could get "lost" by the WSGI
server, let's restore it on the request object like we do for
Content-Length.
FWIW, the WSGI server may also *invent* a Content-Type value. The
default behavior of Python's RFC 822 message class returns a default
media type if Content-Type isn't defined. This is kind of annoying.
But RFC 7231 section 3.1.1.5 does say the recipient may assume a media
type of application/octet-stream. Python's defaults are for
text/plain (given we're using an RFC 822 parser). But whatever.
Differential Revision: https://phab.mercurial-scm.org/D2849
#require docutils gettext
$ $TESTDIR/check-gendoc fr
checking for parse errors